After the recent comeback to the world of aviation, Warren Buffett and his company Berkshire Hathaway are adding sizeable stakes to their investments in a few carefully selected airlines.

In the first quarter of 2017, the company increased its stake in Southwest (+10%) and American (+8%), according to Berkshire’s latest regulatory filing. As of May 2017 Buffet holds $2 billion worth of shares in American and $2.57 billion worth of shares in Southwest.

At the same time, Berkshire decreased the number of shares hold in another major US airline – Delta Air Lines – by 8% to 55 million shares.